Several useful optical systems can be implemented using polarized light. For example, electro-optical devices such as liquid crystal display screens, are illuminated with polarized light and use a pair of polarizers in conjunction with an addressable liquid crystal interlayer to provide the basis for displaying image formation. In the field of photography, polarizing filters have been used to reduce the glare and the brightness of specular reflection. Polarizing filters, circular polarizers or other optical components have also been used for glare reduction in display device screens.
Several different kinds of polarizing film are available for polarizing unpolarized light. Absorbing (dichroic) polarizers have, as an inclusion phase, polarization-dependent absorbing species, often an iodine-containing chain, that are aligned within a polymer matrix. Multilayer reflective polarizers contain a film formed of a stack of many layers of alternating polymer materials. One of the materials is optically isotropic while the other is birefringent, with one of its refractive indices matched to that of the isotropic material. Light of one polarization state is reflected at the interfaces between the layers while light in the other polarization state is transmitted through the polarizer. A diffusely reflecting polarizer can be constructed from inclusions dispersed within a continuous phase matrix. The inclusions are small relative to the width and height of the film. The characteristics of these inclusions can be manipulated to provide a range of reflective and transmissive properties to the film. Either the continuous phase or the disperse phase is birefringent, with one of the refractive indices of the birefringent material matching to the refractive index of the other phase, which is optically isotropic.
Another type of reflective polarizing film is constructed from polymeric fibers within a polymeric matrix, where the polymeric fibers contain interfaces between two materials, one of which is birefringent. Index matching between an isotropic material and one of the two birefringent refractive indices results in one polarization state being transmitted while the other polarization state is diffusely reflected.
One type of polymeric fiber considered for such a polarizer is a concentric multilayer (CML) fiber, which has a series of concentric polymeric layers of alternating materials. This type of fiber is manufactured by coextruding the structure using a complex die and tightly controlled process conditions. Also, the materials used in this type of fiber are limited to those suited for extrusion.